Low-frequency signaling



Nov. 6, 1945.

Tic'l.

H. B. DEAL LOW FREQUENCY S IGNALING Filed Dec. 5, I942 510/0 Peas/val? INVENTOR fli/PMa/v 1.9. 2544.

ATTORNEY signaling s stems, and more nerticuie s-iov.

2,33%,531 now mnenmscs stemmed Harmon B. lice-i, Glen Ridge, 5., e sion Radio @ci'ncmticn of Anicsica, as covnoention oi Delaware Application 5,

My present invention reletes to low frequency 4 commits ing systems of th so-callen alert tyne.

In my application Serial l lo. filed July 23, 1941, Patent No. 2,349,798, dated Fehmiesy wi l, I have disclosed, and claimed, system for modulating a radio frequency cani a low control fyequ 16f), the r c"- ulated caifri e n remote rmelv e uipincnt. and causing the low control my nergy at the receiver to actuate clams c i Ling device concurrently to yendez: the ic ceiver reproduces ineffective. ii change in low frequency at t e tmnsmitter causes device to he in lective while simultaneously ellergizing the remoducer. At the-receiver, these are employed highly selective reeds which tuned to respective low frequencies. These reeds are utilized for the sforeseid control functions.

Now, I have invented a. method oi? utilizing cer= rier energy modulated by low modulation ice quencies in a system for transmitting complete coded messages, end the reeds of the control net work at the receiver equipment being visually oh= served for the message. In cccordcnce with my present system, a plurality of needs of different resonant frequencies are arranged to be selectively actuated by a common diivine source. Certain of the reeds function as message-indicators, while other reeds act as call control switches.

These, and other, objects of my invention will 7 be described in detail in the following specification, it being pointed out that a more specific object of the invention is to improve the 015icienoy of radio signaling systems employing low control modulation frequencies.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claim; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically a circuit organization whereby my invention may be carried into effect.

In the drawing: Fig. 1 shows a receiving system which embodies the invention, s Fig. 2 illustrates the appearance of the viewing ends of the reeds. I

Referring, now, to the accompanying drawing, wherein like reference characters in the two figures designate similar elements, the numeral l indicates, in general, a. signal collector of any inc in a range of cc to so cycles, will be desired The collector may he 9. di c W the mcdulcted comics w L ycle sense.

1 voice, 61?. Hit However, when it is cl iy si system cc more ion 2.1 i to uencies in action lire these pai'ticulec iieci in my application there disclosed one nietho crating various low modulation fi'cquen it is to he understood that the method d in that application may applied to ti mitt-er in the present system. 1 have n such a transmitter, because any form CI Emitter well known in the art may be i To preserve simplicity of description, it sumed that four low modulation ireuuenci used in the p 'esen-t system.

According to my pzesent invention, certain of these low modulation frequencies are to used as message-representative signals, while ethers of the low frequencies are to be employed as callx ing frequencies. By way of specific example, let it be assumed that the 20 and 30 cycle ireouencies are to be used for calling purposes, while the 36 and 24 cycle frequencies are to he employed to convey a message. In such case, one or more of these four low modulation irequem cies will be applied to the carrier at the trans mitter, and then radiated to the various signal collectors.

The signal collector I is connected to the input terminals of a radio receiver 2 of any desired construction, The receiver may be of the superhetcrodyne form, or of the tuned radiofrequency amplifier form, or even of the super-regenerative type. The receiver is schematically represented, since it is only the audio output circult of the receiver which is of interest in connection with my present invention. Let it be assumed, therefore, that the numeral 3 designates the audio transformer which feeds the audio frequency energy of the receiver to the audio ampllfler output'stage 4. As is noted, the amplifler stage 4 is of a. conventional type. and. its output transformer [will be understood as being connected to the voice coil of the usual loud tive indicators.

speaker.- Thus far there has been described a conventional and normal type or receiving system.

In order to secure a response to the low modulation frequencies, the energy of the latter is filtered ofi from the main audio channel at some point prior to the voice coil of the loud speaker. For example, let it be assumed that the low frequency modulation energy is taken off from the grid circuit of amplifier 4, and that the energy is applied through the condenser it to a filter l. The filter 'i' is constructed to pass the low frequencies. This filter, for example, may be a low pass filter which has a cut-off at approximately 10c cycles. Such a filter is easily constructed,

cies other than those in the lowirequency range from passing to the reed-control circuit.

' The reeds are driven by electromagnet 6 whose winding is arrangedin the plate circuit of the amplifier tube 9. Here, again, the amplifier 9 may be of a conventional iorm,'and its grid circuit is shown as including a negative biasing source for the grid of the tube. The grid itself is coupled through a direct current blocking condenser it} to the output terminals of the low pass filter i. It will be understood that the amplifier 9 will amplify those of the low modulation frequencies which were applied to the carrier at the transmitter.

According to my invention, 1 utilize a common support, or mounting, for the four selective reeds. The reeds are indicated by the reference letters A, B, C and D. These four reeds are mechanically resonant to 20 cycles, 30 cycles, 36 cycles and 24 cycles respectively. As is well known to those skilled in the art, each reed consists of thin spring steel. Each reed has one end thereof socured in a metal base H. The base, in turn, is securely fastened to a substantially L-shaped al' mature id. The appearance of the armature is shown in Fig. l, and it will be noted that the vertical section of the armature has an extensive portion it which is positioned adjacent the core of the electromagnet "file armature i2 is metallic, and is composed,

of course, of a magnetic material. The horizontal section or the armature supports the various bases M of the reeds. However, each reed extends substantially beyond the forward edge of the horizontal section of the armature. A steel spring support it is rigidly secured to the vertical section or armature id. The steel spring support it may be secured to a horizontal wooden backing it, it desired. The steel spring support it is grounded through a resistor it oi relatively small magnitude, say for example 20 ohms, while each of reeds A and E is provided on its lower face, adjacent its free end, with a contact point. The

contact point of each reed A or B is adapted to cooperate with a second contact point thereby to provide a switch which closes only when a particular reed vibrates in resonance with an applied low modulation frequency.

The numeral 2t indicates the contacts associated with reed A, and the numeral 2d indicates the contacts associated with reed B. The reeds 'C and D need not have contacts associated therewith, since the function as message-representa- The contacts to are connected to a further switch contact 2!, while the contacts Et' are connected to a switch contact 22. The adjustable arm T is providedior making contact with either of it or 22. In other words, contact arm T functions to select which of the calling and would obviously prevent modulation frequenopen the indicator circuit, if such opening is deof the winding of electromagnet 3!. The lower.

end of the winding is connected to the positive terminal of a direct current source 32' whose ne ative terminal is grounded. The winding of electromagnet Si is by-passed for alternating current by condenser 32. It will, therefore, be seen that current will flow through the winding of electromagnet 3! when switch arm T is on either of El or 22, and when the respective reed contacts it or it? are closed.

--Upon energization of the electromagnet 3! a switch 6b, which is normally spring-biased to open position, is closed. In circuit with the switch so there is included an indicator device,

such as an incandescent lamp et, a direct current energizing source 5 i, and a switch 52. The switch 52 is provided so that the operator may manually sired. This, of course, will render the signaling circuit completely inoperative so long as switch '52 is open. Assuming that the switch has been closed, energization of electromagnet 3| with consequent closing of switch it is necessary to'cause indicator lamp 5% to burn. or course, the lamp 5i? may be replaced by an audible signaling device, such as an electric bell. In general, my invention is not restricted to any particulartype of calling circuit or calling device.

In Fig. 2 I have shown the appearance of the free ends of the reeds A, B, C and D, as well as the visual indicator 5b. The free end of each reed may be provided with a colored tab, as indicated by numeral to in Fig. 2. These tabs may be colored white so that when a reed vibrates violently the efiect of a continuous white bandwill be produced. This effect is indicated by the dotted rectangle iii in Fig. 2. It will be obvious that the reeds may be enclosed in a casing having a windew. and that the reeds may be positioned horizontally in the casing. The free ends of the reeds may be viewed through the window. The casing may, also, have a portion thereof constructed so that the indicator lamp 563 can be viewed therefrom.

To explain the operation of the system, let it be assumed first that the receiver is positioned in the home of an individual, such as an air raid warden, whose calling letter is A. This means that he will adjust his switch arm I to point 21!. When reed A vibrates in response to the reception of a 2d cycle modulation frequency, then the l electromagnet 3! will cause switch 30 to be closed. This indicates visually at lamp ed that a call is being sent through for A to be on the alert for a possible message to follow. Of course, another warden might have the call letter B, and he would filter 1 then armature l3 will be actuated. However, the only reed that will vibrate violently in response to the 20 cycle frequency will be reed A. Reeds B, C and D will not vibrate with any substantial amplitude, because they are highly selective. These other reeds will merely move as part of the general armature assembly. As-

sume, now, that there exists in the winding of electromagnet 8 modulation frequencies of 20 cycles and 30 cycles. In that case the light 50 will burn at the positions of the A individuals, and the A reed will have its free end simulate the dotted rectangle 6|. the locations of the B individuals it will be the free end of the B reed which will simulate the dotted rectangular pattern, while the visual indicator at these positions will be active.

After the calling reed has been actuated, there may now be applied at the transmitter the C I and/or D modulation frequencies. Let it be assumed that C and D reeds are to be actuated by applying concurrently the 36 cycle modulation and 24 cycle modulation to the carrier. In such case there will flow through the winding of eiec tromagnet 3 the currents of both these modulation frequencies, and this will cause violent VibZ'E-c tion of both reeds C and D. The observer will then see both free ends of these reeds simulate the rectangular pattern. They will then know, in accordance with a predetermined code, that a certain message has been sent to them. It is to On the other hand, at

be understood that subsequent to the calling signai, there will be included that particular calling-reed as part of the message signals along with reeds C and D. Y

In other words, assume that the 20 cycle modulation frequency has been transmitted so as to cal1 all individuals A to stand by for messages.

Thereafter, the 20 cycle frequency can be used in conjunction with the 36 and 24 cycles so as 40 to provide messages by means of the vibrations of reeds A, C and D. This would also be true for the B reed. It will, therefore, be seen that after transmission of a call frequency, rather complete ,coded messages can be sent by visual observation of the reeds. For example, after calling individuals A, reeds A, C and D simultaneously vibrated could mean: Stand by for further ther instruction. Finally, self could mean that the system could be turned instructions; reeds C and D vibrated concurofl', or that it was'an All clear" signal.

It will be understood that actuation of switch ll may, if desired, render the circuit to the voice coil ineffective. The utility of such arrangement would reside in the fact that interruption of sound reproduction would focus attention on the reeds and indicator. Preferably, however, it is desired to keep the sound channel continually clear so that instructions can readilybe given to the called individuals. or course, the codes of signals can be changed periodically. Indeed, at periodic intervals the message reeds could be changed over to function as call reeds, while the reeds A and B could function as message reeds. The circuit changes required for such an interchange are obvious.

While I have indicated and described a sys tem for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended cla What I claim is:

In a reed signaling system, a plurality of reeds of different frequencies, a common magnetic support for said reeds, said magnetic support having an extension, a source of currents of frequencies corresponding to said read frequencies, an electromagnet responsive to the currents for actuating said support extension thereby to vibrate solely those reeds corresponding in frequency to the frequencies of the said currents, an indicator circuit including a normally open switch, a control circuit for the switch including an electromagnet positioned adjacent the normally open switch to actuate the latter upon energization of the control circuit, and switch means for selectively associating desired ones of 

